Re: [PATCH 6/8] dmaengine: tegra: Use iommu-map for stream ID

[Frank Li]

On Tue, Feb 17, 2026 at 11:04:55PM +0530, Akhil R wrote:
> Use iommu-map, when provided, to get the stream ID to be programmed
> for each channel. Register each channel separately for allowing it
> to use a separate IOMMU domain for the transfer.
>
> Channels will continue to use the same global stream ID if iommu-map
> property is not present in the device tree.
>
> Signed-off-by: Akhil R <akhilrajeev@xxxxxxxxxx>
> ---
>  drivers/dma/tegra186-gpc-dma.c | 62 +++++++++++++++++++++++++++-------
>  1 file changed, 49 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/dma/tegra186-gpc-dma.c b/drivers/dma/tegra186-gpc-dma.c
> index ce3b1dd52bb3..b8ca269fa3ba 100644
> --- a/drivers/dma/tegra186-gpc-dma.c
> +++ b/drivers/dma/tegra186-gpc-dma.c
> @@ -15,6 +15,7 @@
>  #include <linux/module.h>
>  #include <linux/of.h>
>  #include <linux/of_dma.h>
> +#include <linux/of_device.h>
>  #include <linux/platform_device.h>
>  #include <linux/reset.h>
>  #include <linux/slab.h>
> @@ -1403,9 +1404,12 @@ static int tegra_dma_program_sid(struct tegra_dma_channel *tdc, int stream_id)
>  static int tegra_dma_probe(struct platform_device *pdev)
>  {
>  	const struct tegra_dma_chip_data *cdata = NULL;
> +	struct tegra_dma_channel *tdc;
> +	struct tegra_dma *tdma;
> +	struct dma_chan *chan;
> +	bool use_iommu_map = false;
>  	unsigned int i;
>  	u32 stream_id;
> -	struct tegra_dma *tdma;
>  	int ret;
>
>  	cdata = of_device_get_match_data(&pdev->dev);
> @@ -1433,9 +1437,12 @@ static int tegra_dma_probe(struct platform_device *pdev)
>
>  	tdma->dma_dev.dev = &pdev->dev;
>
> -	if (!tegra_dev_iommu_get_stream_id(&pdev->dev, &stream_id)) {
> -		dev_err(&pdev->dev, "Missing iommu stream-id\n");
> -		return -EINVAL;
> +	use_iommu_map = of_property_present(pdev->dev.of_node, "iommu-map");
> +	if (!use_iommu_map) {
> +		if (!tegra_dev_iommu_get_stream_id(&pdev->dev, &stream_id)) {
> +			dev_err(&pdev->dev, "Missing iommu stream-id\n");
> +			return -EINVAL;
> +		}
>  	}
>
>  	ret = device_property_read_u32(&pdev->dev, "dma-channel-mask",
> @@ -1449,7 +1456,7 @@ static int tegra_dma_probe(struct platform_device *pdev)
>
>  	INIT_LIST_HEAD(&tdma->dma_dev.channels);
>  	for (i = 0; i < cdata->nr_channels; i++) {
> -		struct tegra_dma_channel *tdc = &tdma->channels[i];
> +		tdc = &tdma->channels[i];
>
>  		/* Check for channel mask */
>  		if (!(tdma->chan_mask & BIT(i)))
> @@ -1469,10 +1476,6 @@ static int tegra_dma_probe(struct platform_device *pdev)
>
>  		vchan_init(&tdc->vc, &tdma->dma_dev);
>  		tdc->vc.desc_free = tegra_dma_desc_free;
> -
> -		/* program stream-id for this channel */
> -		tegra_dma_program_sid(tdc, stream_id);
> -		tdc->stream_id = stream_id;
>  	}
>
>  	ret = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(cdata->addr_bits));
> @@ -1517,20 +1520,53 @@ static int tegra_dma_probe(struct platform_device *pdev)
>  		return ret;
>  	}
>
> +	list_for_each_entry(chan, &tdma->dma_dev.channels, device_node) {
> +		struct device *chdev = &chan->dev->device;

why no use
	for (i = 0; i < cdata->nr_channels; i++) {
		struct tegra_dma_channel *tdc = &tdma->channels[i];
> +
> +		tdc = to_tegra_dma_chan(chan);
> +		if (use_iommu_map) {
> +			chdev->coherent_dma_mask = pdev->dev.coherent_dma_mask;
> +			chdev->dma_mask = &chdev->coherent_dma_mask;
> +			chdev->bus = pdev->dev.bus;
> +
> +			ret = of_dma_configure_id(chdev, pdev->dev.of_node,
> +						  true, &tdc->id);
> +			if (ret) {
> +				dev_err(chdev, "Failed to configure IOMMU for channel %d: %d\n",
> +					tdc->id, ret);
> +				goto err_unregister;
> +			}
> +
> +			if (!tegra_dev_iommu_get_stream_id(chdev, &stream_id)) {
> +				dev_err(chdev, "Failed to get stream ID for channel %d\n",
> +					tdc->id);
> +				goto err_unregister;
> +			}
> +
> +			chan->dev->chan_dma_dev = true;
> +		}
> +
> +		/* program stream-id for this channel */
> +		tegra_dma_program_sid(tdc, stream_id);
> +		tdc->stream_id = stream_id;
> +	}
> +
>  	ret = of_dma_controller_register(pdev->dev.of_node,
>  					 tegra_dma_of_xlate, tdma);
>  	if (ret < 0) {
>  		dev_err_probe(&pdev->dev, ret,
>  			      "GPC DMA OF registration failed\n");
> -
> -		dma_async_device_unregister(&tdma->dma_dev);
> -		return ret;
> +		goto err_unregister;
>  	}
>
> -	dev_info(&pdev->dev, "GPC DMA driver register %lu channels\n",
> +	dev_info(&pdev->dev, "GPC DMA driver registered %lu channels\n",
>  		 hweight_long(tdma->chan_mask));
>
>  	return 0;
> +
> +err_unregister:
> +	dma_async_device_unregister(&tdma->dma_dev);

Can you use dmaenginem_async_device_register() to simple error path?

Frank
> +	return ret;
>  }
>
>  static void tegra_dma_remove(struct platform_device *pdev)
> --
> 2.50.1
>